This invention relates generally to the field of radio frequency (RF) shielding systems, and more specifically to the design of door systems for RF enclosures.
RF sealing is employed in test and production environments where the amount of radiation emitted or absorbed by an electronic device must be closely controlled. Excess RF exposure can lead to erroneous test results, or in production and operational environments, degrade the performance of equipment sensitive to the emitted radiation. RF sealing is also important when an electronic component emits sufficient radiation to impact the performance of other proximate electronic components. In this second case, RF sealing isolates the source of radiation, while the first case may be used to isolate sensitive RF components. RF sealing requires close attention wherever an opening is required. RF seals that are dependent on compressed gaskets perform relative to the amount of compression on the gasket. Data provided by Instrument Specialties(copyright), for instance, clearly relate isolation quality to gasket compression. This is a simple problem for access panels where one can achieve the proper level of gasket compression using screws. However, an active opening such as a door-RF enclosure interface, that employs a similar seal, induces additional design difficulties in order to achieve uniform seal compression. The compression uniformity must extend around the entire length of the seal. Furthermore, the compression of the gasket induces reactive forces that cause elastic materials to deflect. The reactive deflection of components causes non-uniformity in the gaskets compression and as a result degrades the RF seal quality.
When the RF seal to the RF enclosure is a drawer door, several more design considerations must be included. The drawer door must be rigid enough to support a load and ensure a uniform seal across the length of the door-enclosure interface. One technique to address this rigidity requirement is to use precision machining and rigidity of mating components. This approach is costly, due to the price of precision machining. Other systems accept an RF seal with non-uniform compression in order to save the expenses associated with the precision machining. However, non-uniform compression results in non-uniform RF isolation. In addition to the RF seal requirements, the drawer door must be rigid enough to withstand loads along the axis of the drawer door as well as perpendicular to the door axis. For this reason, drawer door RF seal systems do not generally employ a gimbal system on the door. The use of a gimbal system allows the door to xe2x80x9cfloatxe2x80x9d on one or more axes. User feedback of a floating door exposes a perceived lack of rigidity and associated poor quality.
The perceived lack of rigidity and poor quality has hindered the implementation of a floating door system.
Therefore, there is an unmet need in the art for a drawer door RF seal system that is stable, able to support uniform seal compression for superior RF isolation, inexpensive to manufacture, and is compatible with existing drawer door interfaces.
The floating drawer door system of the present invention establishes structural stability through the use of three points of contact between the drawer door and the drawer base, whenever the drawer door is not engaged with the sealing portion of the associated frame. As the door approaches the frame, two of the three contact points are deactivated, allowing the drawer the freedom to pivot from a point near the seal centroid. A pivoting gimbal system provides the primary contact point. By using the gimbal, employing two-axes of rotation, rotation in the third axis is restricted. Two spring plungers are employed, referencing into conical detents, to provide the remaining two contact points. The implementation of the spring plungers is twofold. Retracting the plungers from the detents allows the drawer door gimbal to apply the closing force at the centroid of the gasket interaction line.
As the door approaches the frame, two of the three contact points are deactivated. This occurs when the spring plungers are retracted, by pushing them out of their detents. To do this, a pin is employed to apply a force against the nose of the plunger. The pin is displaced by a trigger mechanism. The trigger is displaced as it contacts a dowel pin installed in the frame. The dowel pin is strategically positioned such that it cams the trigger just as the door approaches its mating surface. One activation pin, one dowel pin, and one trigger are employed for each of the two spring plungers according to an embodiment of the present invention.
The release of two of the three contact points allows the drawer door to float in order to utilize the functionality of the two-axis gimbal system. This floating system allows the mating surfaces to be parallel and not deflect as the forces resulting from gasket compression are applied. To help achieve this, the mating force is applied to the centroid of the force line. The gimbal prevents distortion due to off-center loading, by its location at the centroid through which the load is applied. The floating gimbal system also allows the door to float in order to maintain force uniformity as the compression seal is applied.